Ruby on Rails Wednesday, July 12, 2017


I looked through your code and I'm not sure you have answered my question.

Let me try to clarify.  There is a difference between a Devise role and a Postgres role.  A devise role will control access to Rails functionality.  For example, one can restrict access to a Rails controller method using Devise.

A Postgres role ( ) is a completely different animal. I quote and modify what is written there:
Database roles are conceptually completely separate from operating system [and Devise!] users.

I _think_ I need to do something like "sudo -i -u SomeOtherPostgresUserName" but I want to do it inside Rails so I can connect to databases as user SomeOtherPostgresUserName.

Can you share how you did the "give each RoR user the ability to write their own SQL statements "? I may want to do the same.

Here is the code I use.  RalphSql.exec_sql is what you want.  RalphSql.get_column_names_from_table is a function I find useful for other obvious purposes.
class RalphSql
def self.exec_sql(sql_text)
# Return an array of records
return ActiveRecord::Base.connection.execute(sql_text)
rescue Exception => e
if ralph_test_byebug
raise e

# See
def self.get_column_names_from_table(postgres_table_name)
= %Q[SELECT column_name FROM information_schema.columns WHERE table_name = '#{postgres_table_name}';]
# byebug if ralph_test_byebug
= RalphSql.exec_sql(sql)  # pg_result.class == PG::Result
= pg_result.values
# byebug if ralph_test_byebug


I use devise and cancancan for login and roles.

I use pundit

On Wednesday, July 12, 2017 at 4:51:32 AM UTC-6, David Gleba wrote:

I use devise and cancancan for login and roles.

In my little rails app generator project:  there are scripts for this. Even if you don't use the scripts, they document exactly how to implement it in that case.

look at:  

When I am learning something like this I strip the scripts down to just what is needed to create an app with the feature I am studing.

I am not sure about the  "give each RoR user the ability to write their own SQL statements ".
Is that just a model/view/controller in your app? If so, the above should work for that too.

Can you share how you did the "give each RoR user the ability to write their own SQL statements "? I may want to do the same.

On Tuesday, July 11, 2017 at 11:39:13 PM UTC-4, Ralph Shnelvar wrote:
I have a database with a large table.

I have several users each of whom should have read-only rights to the large table but has read/wrtie rights to their own table(s) but not to each others table(s).

Adding to the complication, I want to give each RoR user the ability to write their own SQL statements against the large table as well as their own table(s).  I have successfully implemented being able to have them enter sql statements and create results they can view and/or download.  Doing that is not my question.

I want to make sure each of my "readonly" users can't modify any tables they are not authorized to see and/or change.

So,I guess, I want to change Postgres roles within Rails.  Any guidance would, of course, be appreciated.

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